Re: [PATCH v4 1/5] expand-on-first-boot: support resizing a btrfs

["Roberto A. Foglietta" <roberto.foglietta@gmail.com>]

On Tue, 13 Dec 2022 at 11:15, <henning.schild@siemens.com> wrote:
>
> From: Henning Schild <henning.schild@siemens.com>
>
> This adds support for resizing btrfs filesystems if they are in that
> last partition. It also prepares for potentially other filesystems to
> come in the future by introducing a switch-case.
>
> The mounting logic is taken from the systemd-growfs patches we had to
> revert again. Some filesystems need to online for resizing, but in order
> to find the filesystem of a partition (without udev) mounting it and
> letting the kernel detect seems a good idea.
>

It is possible to avoid the udevadm settle constraints only because
the boot device [1] is the same as the rootfs device. The boot device
should be mapped by the kernel at boot time, so it would be available
but not necessarily present in /dev partition if this has no static
links or devfs mounted at the time of mount. If udevd is the demon
that we choose to populate the /dev then it would be better to wait
until it settles down. The stats about boot time on different
platforms will show that only hardware slow to detect has a larger
boot time.

[1] in some embedded devices the boot device is an internal and small
device dedicated to the boot while the rootfs is on a separate
plug-able device.

I have no clue how this would matter in the case of ISAR.

Best regards, R-